Method of purifying fatty acids



Patented Apr. 6, 1943 METHOD OF PURIFYING FATTY ACIDS Waldo L. Semen, Silver Lake, Ohio, assignor, by

mesne assignments, to The B. F. Goodrich Company, Akron, Ohio, a corporation of New York No Drawing. Application April 24, 1941, Serial No. 390,137

6 Claims.

This invention relates to the purification of fatty acids and fatty acid derivatives and has as its principal object the preparation of fatty acids and fatty acid derivatives of high purity from fatty acids or alkali metal salts of fatty acids contaminated with materials which cannot readily be separated therefrom by distillation.

In many industrial processes, fatty acids and fatty acid derivatives of high purity are required. In emulsion polymerizations, for instance, soap is often employed as the emulsifying agent. The presence of even small amounts of impurities may inhibit or alter the course of the polymerization. Consequently, fatty acids of high purity are required as a raw material for making the soap. The soap may be recovered by coagulation of the latex-like products of emulsion polymerization and removal of the synthetic rubber, but the soap as well as the fatty acids which may be obtained therefrom by hydrolysis are often contaminated and unfit for further use in emulsion polymerizations without purification. One ordinary source of contamination is the antioxidant which is ordinarily added to the latex before coagulation to preserve the synthetic rubber. Although most of the antioxidant remains in the rubber, enough is ordinarily retained in the soap to inhibit any subsequent polymerization in which the soap is present.

Various methods of removing the antioxidant from the soap have been tried, but they have in general been unsuccessful. Such small amounts of antioxidant are deleterious to the polymerization that removal by solvent extraction is impractical. Attempts have been made to hydrolyze the soap and separate the fatty acid and anti.- oxidant by fractional distillation. This method has in general met with failure because of the proximity of the boiling points of the common fatty acids and the antioxidants ordinarily used. It is also undesirable to select antioxidants hav ing such low boiling points that they may readily be separated from the fatty acids by fractional distillation, since volatile antioxidants evaporate from the rubber,

By the method of this invention, contaminated fatty acids are treated with reactants affecting the --OH of the --COOH group to form lowerboiling derivatives; 1. e., compounds exhibiting boiling points lower than fatty acids, and these lower-boiling derivatives are then separated from the contaminants by fractional distillation. Although a number of derivatives may be prepared, the lower alkyl esters are in general the most satisfactory and most feasible commercially. The methyl and ethyl esters are ordinarily formed, although other lower alkyl esters in which the alkyl group preferably contains not more than five carbon atoms may be formed if desired. Other lower-boiling derivatives such as the acid chlorides may be prepared instead of the esters.

As a specific example of an embodiment of this invention, it will be shown how sodium myristate contaminated with phenyl-betanaphthylamine was purified. Sodium myristate was employed during the emulsion copolymerization of butadiene and acrylonitrile. A phenyl-betanaphthylamine emulsion was then added to the latex-like product. It was found that the sodium myristate remaining after coagulation and separation of the synthetic rubber contained too much inhibitor to be used as the emulsifying agent in another charge, The myristate acid was liberated from the soap solution by acidification with sulfuric acid. Careful fractional distillation through a 12-inch column containing a coil of aluminum wire did not separate the myristic acid from the phenyl-beta-naphthylamine, although the boiling point of the amine at 1.8 mm. pressure is over 200 C. and the boiling point of the acid is 148-153 C.

One mol (228.4 g.) of the contaminated myristic acid was dissolved in 250 cc. of synthetic methanol. A stream of hydrogen chloride was passed through the solution. The solution became cloudy and the temperature rose from 21 C. to 41 C. The solution was then heated to 52 C. whereupon two layers formed. The passage of hydrogen chloride was continued while the temperature was allowed to fall slowly to 37 C. The two layers were separated, and after removal from the top layer of the hydrogen chloride and methyl alcohol by washing with water, 225 g. of crude methyl myristate remained. When the crude material was distilled through the 12-inch column previously mentioned, the fraction collected at 116-1l8 C. at 1.8 mm. pressure was colorless methyl myristate free from phenyl-beta-naphthylamine and other inhibiting contaminants. The methyl myristate was completely converted to sodium myristate by heating with an equimolar quantity of sodium hydroxide for an hour at C. The sodium myristate so formed was found to be as satisfactory an emulsifying agent for emulsion polymerization as the material employed at the beginning of the experiment. If the free myristic acid is desired, it may be formed by acidifying the sodium myristate solution or directly from the methyl ester by acid catalyzed hydrolysis in the presence of a quantity of hot water.

Other methods of esterifying the fatty acid may be employed than the one described. The contaminated myristic acid may be refluxed with methyl or ethyl alcohol in the presence of sulfuric acid, for instance, to form an alkyl myristate which may be separated as above from the contaminant by fractional distillation.

Although the method of this invention may be applied to any of the fatty acids, it is ordinarily employed to obtain free fatty acids or alkali metal salts of fatty acids containing between 12 and 18 carbon materials, these materials being most useful in emulsion polymerization.

Although I have herein disclosed a specific embodiment of my invention, I do not intend to limit the invention solely thereto for many variations and modifications are within the spirit and scope of the invention as defined in the appended claims.

I claim:

1. The method of separating a fatty acid containing between 12 and 18 carbon atoms from a diarylamine which comprises forming a lowerboiling alkyl ester of the fatty acid and separating the ester and the diarylamine by fractional distillation.

2. The method of forming uncontaminated soap from a fatty acid containing a diarylamine which comprises forming a lower-boiling alkyl ester of the fatty acid, separating the ester and the diarylamine by fractional distillation, and treating the ester to form soap free from the diarylamine.

3. The method of forming uncontaminated soap from a fatty acid containing phenyl-betanaphthylamine which comprises forming the methyl ester of the fatty acid, separating the ester and the phenyl-beta-naphthylamine by fractional distillation, and reacting the ester with sodium hydroxide to form soap free from phenylbeta-naphthylamine.

4. The method of separating a fatty acid containing between 12 and 18 carbon atoms from phenyl beta naphthylamine which comprises forming a lower-boiling compound of the fatty acid through a reaction of the --OH of the -COOH group and separating the derivative and the phenyl-beta-naphthylamine by fractional distillation.

5. The method of forming uncontaminated so dium myristate from myristic acid containing phenyl beta naphthylamine which comprises forming methyl myristate from the myristic acid, separating the methyl myristate and the phenylbeta-naphthylamine by fractional distillation, and reacting the methyl myristate with sodium hydroxide to form sodium myristate.

6. The method of forming uncontaminated myristic acid from myristic acid contaminated with phenyl-beta-naphthylamine which comprises forming methyl myristate from the myristic acid, separating the methyl myristate and the phenyl-beta-naphthylamine by fractional distillation, and hydrolyzing the methyl myristate with water to form free myristic acid.

WALDO L. SEMON. 

